Composite electrodes for directional crystal devices



March 3, 1959 P. GUNTHER ET AL COMPOSITE ELECTRODES FOR DIRECTIONALCRYSTAL DEVICES Filed Feb. 1, 1954 Paul G22 E022 g y S 6 0 m5 %r neUnited States Patent O COMPOSITE ELECTRODES FOR DIRECTIONAL CRYSTALDEVICES Paul Giinther and Franz Kerkhoif, Munich, Germany, assignors toSiemens & Halske Aktiengesellschaft, Munich, Germany, a corporation ofGermany Application February 1, 1954, Serial No. 407,196

Claims priority, application Germany February 27, 1953 11 Claims. (Cl.317235) This invention is concerned with composite electrodes fordirectional devices comprising semi-conductors, for example, transistorsand the like.

Composite electrodes for the purpose and of the type noted above aregenerally known. It is likewise known to form on such electrodespreferably point-shaped or knife-edge contacts of a hard core which isprovided with a coating of another generally softer material, the latterbeing more suitable than the core material to form electrical contactengagement with a semi-conductor crystal. Such a known electrode may,for example comprise a tungsten wire plated with platinum. The drawbackof such structure is that it is impossible to provide upon tungsten asufliciently uniform platinum coating and that it is consequentlyimpossible to produce such electrodes with the required uniformity inthe course of customary mass production processes.

It has been found by research lying in back of the invention that theabove mentioned drawbacks can be avoided by using other particularmaterials. In accordance with the invention, electrodes of thepreviously indicated type which comprise at least two differentmaterials, for example, a core or carrier and a coating, are made ofmetals from the first, fourth, fifth and/or eight groups of the periodictable of elements. More specifically a hard material as for exampleniobium, tantalum, iron or alloys of such materials, for example, hardbronze of the type of phosphor-beryllium-bronze or the like may be usedprimarily for the core of the electrode; and for the coating may be usedprimarily materials of high output capacity, for example, rhodium,palladium, iridium, also platinum or, under some circumstances alloys ofthese materials. In the case of using in a transistor a plurality ofelectrodes, for example, two or three electrodes, the selection of thematerial for the surface coating will depend upon whether the electrodeis to be employedas a collector or an emitter.

The invention will now be described with reference to the accompanyingdrawings showing in diagrammatic representation examples thereof. Inthese drawings,

Fig. 1 shows a germanium crystal coacting with a single point contactelectrode; and

Fig. 2 illustrates a transistor comprising a germanium crystal coactingwith two point contact electrodes.

In Fig. 1, numeral 1 indicates the germanium crystal. In contactengagement with the surface of the crystal is a point electrodecomprising a wire 2 of phosphorberyllium-bronze provided with a platinumcoating 3. The electrode is produced by providing upon the bronze wire,for example, in an alkaline ammonia phosphorous platinum bath ofplatinum coating in galvanic manner.

Fig. 2 shows a transistor comprising a germanium crystal 4 coacting withtwo point contact electrodes 5 2,876,400 Patented Mar. 3, 1.959

ice.

2 and 6.- Bet'ween the electrodes, a p-n layer is provided in a knownmanner. The electrode 5 is made like the electrode of Fig. 1, comprisinga bronze core with a platinum coating 3. The other electrode 6 comprisesa steel core '7 covered by a copper coating 8.

The coatings may be applied or provided in different manner thangalvanic, for example, by vaporization, by cathode vaporization, or inmechanical manner, for example, by spraying or rolling. Burning such asis usually applied in the production of mirrors, ceramics, etc., isrecommended for mass production.

What is believed to be new and desired to have protected is defined inthe appended claims.

We claim:

1. A transistor comprising a crystal, in electrode in point contact withsaid crystal, said electrode including a core and a coating surroundingsaid core, said core formed from one or more metals of the groupconsisting of niobium, tantalum, iron, copper, tin, zinc, phosphorous,beryllium and alloys of the aforesaid metals, said coating formed fromone or more metals of the group consisting of rhodium, palladium,iridium, platinum and alloys of the aforesaid metals, and said coatingof said electrode in point contact with said crystal.

2. A transistor according to'claim 1, wherein said core of the electrodecomprises a hard bronze of the type of phosphor-beryllium-bronze.

3. A transistor according to claim 1, wherein said core of the electrodeis formed of a hard bronze of the type of phosphor-beryllium-bronze, andsaid coating is formed of platinum.

4. A transistor comprising a crystal, at least two electrodes in pointcontact with said crystal, p-n layer provided in said crystal betweenthe electrodes, one of said electrodes comprising aphosphor-betyllium-bronze core and a platinum coating, the other of saidelectrodes comprising a steel core and a copper coating, and saidcoatings of said electrodes in point contact with said crystal.

5. A composite electrode for a directional crystal device, saidelectrode provided with a point at one end for point contact with acrystal and comprising a core and a coating surrounding said core, saidcore formed from one or more materials of the group consisting oftantalum, phosphor-beryllium-bronze and steel, said coating formed fromone or more materials of the group consisting of the elements of groupeight of the periodic table of elements and consisting of rhodium,palladium, iridium and platinum.

6. A composite electrode according to claim 5, wherein said compositeelectrode may be used in a diode.

7. A composite electrode according to claim 5, wherein said compositeelectrode may be used as an emitter in a transistor.

' 8. A composite electrode for a directional crystal device saidelectrode formed with a point at one end for point contact with acrystal and comprising a steel core and a copper coating surroundingsaid core.

9. A composite electrode for use as a collector, said electrodecomprising a core and a coating surrounding said core, said core formedfrom one or more materials of the group consisting of tantalum,phosphor-berylliumbronze and steel, and said coating comprising one ormore materials of the group consisting of copper and tin.

10. A semi-conductor device of the transistor type including adirectional crystal, a composite electrode for point contact with saiddirectional crystal, said composite electrode comprising a phosphorberyllium-bronze coreand a platinum coating surrounding saidcore, and

References Cited in the file of this patent UNITED STATES PATENTS TaylorMay 5, 1942 Ohl June 25, 1946 Eitel Mar. 18, 1947 Woodyard Nov. 14, 1950Beck Sept 25, 1951 Carrnan et a1. Dec. 31, 1957

1. A TRANSISTOR COMPRISING A CRYSTAL, IN ELECTRODE IN POINT CONTACT WITHSAID CRYSTAL, SAID ELECTRODE INCLUDING A CORE AND A COATING SURROUNDINGSAID CORE, SAID CORE FORMED FROM ONE OR MORE METALS OF THE GROUPCONSISTING OF NIOBIUM, TANTALUM, IRON, COPPER, TIN, ZINC, PHOSPHOROUS,BERYLLIUM AND ALLOYS OF THE AFORESAID METALS, SAID COATING FORMED FROMONE OR MORE METALS OF THE GROUP CONSISTING OF RHODIUM, PALLADIUM,IRIDIUM, PLATINUM AND ALLOYS OF THE AFORESAID METALS, AND SAID COATINGOF SAID ELECTRODE IN POINT CONTACT WITH SAID CRYSTAL.